The most basic extrusions are square and there will be a central hole and one or more T slots for attaching things. In general, the extrusion will be like a square or a rectangle.

There isn’t just a single kind of extrusion, but they all share some common features. Extrusion Geometry A typical 2020 profile A fantastic example of this are all of the brackets and retaining parts Roger Cheng covered in his guide How to Build Anything Out of Aluminum Extrusion and 3D Printed Brackets. One thing that has made working with extrusions easier is that you can 3D print just the bracket you need in many cases instead of buying an exotic bracket or having to stock a lot of different items. You can think of it as something akin to an adult Erector set. There are brackets and special nuts and a variety of accessories. However, what you do need is a lot of special parts. In some cases, you may want to tap some holes - either that already exist or those you freshly drilled. In general, all you need is a way to cut the extrusion square (or, buy it in the lengths you want) and a way to drill holes in the relatively soft aluminum. But having stock inexpensive aluminum is both strong and convenient. After all, it isn’t hard to build a box out of wood or even aluminum stock. If you are handy enough, of course, you can build all of those things without resorting to aluminum extrusion. Why Extrusions? Hackaday’s own Roger Cheng shows the versatility of aluminum extrusion and shares a wealth of tips he developed for his Sawppy the Rover project. If you need a custom workbench, a light fixture, or even a picture frame, you can build anything you like using extrusions. There seems to be a lot of people using them, for example, to build custom fixtures inside vans. But you can use it anywhere you need a sturdy and versatile frame. We use extrusions to create frames for 3D printers, laser cutters, and CNC machines.

Oddly, there doesn’t seem to be an official standard, but it is so common that there’s usually not much variation between different vendors.

Of course, aluminum extrusions aren’t made from modeling clay, but usually 6105-T5 aluminum. You push some material out through a die to make a shape. If you ever had a Play-Doh Fun Factory as a kid, then you know about extrusions. However, it is one thing to assemble a kit with some extrusions and another thing to design your own creations with the material. T-slot extrusions used to be somewhat mysterious, but today they are quite common thanks to their use in many 3D printers.

8020 t slot cover